1. Field of the Invention
The present invention relates to a method for measuring free radical, particularly to a method for measuring free radical based on conductivity change of conductive polymer.
2. Description of the Prior Art
Oxidative stress is currently an important research topic and is believed to be relevant to tumors, cancers, Parkinson's disease, and aging. Oxidative stress is induced by reactive oxygen species (ROS), including hydrogen peroxide (H2O2), hydroxyl radical (OH.), superoxide anion (O2.−) and singlet oxygen (O2.).
Hydroxyl radical was reported to be the most reactive free radical. Hydroxyl radical was found to be able to damage DNA, RNA, proteins and lipids, leading to abnormal cell response and cell apoptosis in physiological and pathological environment. Hydroxyl radicals can be generated by Fenton reaction or Haber-Weiss reaction in vivo. Among these ROS, hydrogen peroxide is much easier to be detected due to its longest life-time. However, detecting radicals, especially for hydroxyl radicals, is challenging due to its very short life-time (˜μs).
Several techniques are utilized to detect hydroxyl radicals. Electron spin resonance spectroscopy (ESR) is a typical technique, which can detect molecules with unpaired electron by characterizing the electron paramagnetic spectrum. However, the life-time of hydroxyl radicals is too short to be detected directly by ESR. Instead, a spin trap molecules, such as 5,5-dimethyl, 1-pyrroline N-oxide (DMPO), is employed to bind with hydroxyl radicals to form a complex, which is still a radical but has a longer half-life to be detected by ESR.
Fluorescence spectroscopy has also frequently been used to quantify hydroxyl radicals by the oxidation of fluorescent probes with hydroxyl radicals to either enhance or quench fluorescence signals. Chemiluminescence (CL) is enhanced with the chemiluminogenic probes reacting with hydroxyl radicals. Ultraviolet-visible spectroscopy is based on the absorbance change of a probe molecule after reacting with hydroxyl radicals, such as Br−, Crocin, Ferrocyanide, or Rhodamine B. High pressure liquid chromatography (HPLC) has also been employed for hydroxyl radical detection. The above mentioned techniques are currently the most commonly used methods for detecting hydroxyl radicals.
However, these techniques all require extensive instruments, and on the other hand, they also face a problem that is the degradation of probe molecules during the measurement. To effectively reduce the high cost of hydroxyl radical detection, electronic miniaturized microsensors might be good candidates for low cost detection. Electrochemical sensors and QCM sensor were reported to detect hydroxyl radicals. Compared to the typical techniques, including ESR, Fluorescence, CL, UV-Vis, and HPLC, electronic microsensors were quite few and seldom reported for free radical detection. However, due to the great advance in microfabrication technique, electronic microsensors can be very cost-effective, and in the meantime, with comparable sensitivity and limit of detection (LOD), compared to those of typical measurements. Thus, there is a great interest and demand to develop simple, cost-effective, and highly sensitive electronic microsensors for hydroxyl radical detection.